In modern agriculture, insecticides are extensively used to manage insect populations and protect crops. Despite heavy regulation, misuse occurs, meaning that insecticides sometimes make their way into the surrounding environment via the air, water, or soil, and ultimately entering the food chain. Once present, insecticides can have adverse health effects on humans in the proximity, or with the globalization of industrial farming, could be distributed over a wide area.
The common insecticide, fipronil, provides a recent example of the problem. Fipronil was shown to have contaminated millions of eggs, which were subsequently distributed to over 17 countries. In July 2017, an announcement was made that fipronil was mixed with another formulation, and applied to chickens to guard against ticks, lice, and fleas. In some cases, this led to both the poultry and their eggs containing over 200 times the European Union’s maximum residue levels (MRL) for fipronil, and its metabolite, fipronil sulfone. Due to this contamination, a quick and reliable method for determining the presence and concentration of the insecticide in eggs, egg products, and potentially chicken meat is required.
The QuEChERS Method
In order to begin the analysis, the contaminants must first be extracted from the egg matrix. Traditional approaches of tainted food sample extraction involve varied, costly, and time-consuming techniques, which require large amounts of solvents. A promising process that has overcome these limitations is QuEChERS extraction (which is in reference to it being Quick, Easy, Cheap, Effective, Rugged, and Safe). First developed in 2003 by Anastassiades et al., this method takes approximately 15 minutes, and allows for high throughput analysis. The runtime even has the potential to be shortened to eight minutes if used in conjunction with a Thermo Scientific Accurse a Q column. This extraction approach is highly robust and reliable, and up to 100 egg samples can be analyzed without the need for the system to undergo maintenance. The availability of the QuEChERS method is key given the scale of the contamination issue; millions of eggs could potentially require analysis to ensure safety.
To comprehensively monitor the levels of different types of insecticides present in eggs, both liquid chromatography (LC) and gas chromatography (GC) analysis should be performed on the extracted samples. By performing both techniques, LC will ensure that all soluble compounds present in the sample will be analyzed, whereas GC will analyze all volatile compounds and gaseous mixtures. A study has shown that store-bought eggs, can be spiked with fipronil, fipronil sulfone, or fipronil sulfinyl, extracted with the QuEChERS method, and effectively examined with LC or GC.
Using the QuEChERS method in both cases, users take the spiked and homogenized egg sample, add water, acetonitrile, magnesium and sodium salts, then agitate and centrifuge the solution. The whole process is performed in a fraction of the time of alternative techniques and uses a small amount of a single solvent. After the QuEChERS extraction, the next step is to perform a dispersive solid phase extraction (SPE) which removes the excess water, and finally, the sample can be analyzed by either liquid chromatography (LC) or gas chromatography (GC) in conjunction with a triple quadrupole mass spectrometry (MS/MS) system.
New levels of detection for fipronil with LC-MS/MS & GC-MS/MS
Both the LC-MS/MS and GC-MS/MS systems can accurately detect the presence of the insecticide contaminant with excellent sensitivity and selectivity. During testing protocols, fipronil, fipronil sulfone, and fipronil disulfonyl were all detected at concentrations down to 0.2 micrograms per kilogram of egg sample. This concentration is five times lower than the EU maximum residue levels. These methods, therefore, show their suitability for the sensitive detection of fipronil contaminated eggs and have the potential to determine contaminants within other tainted food sources.
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